Subtypes in unions aren't working correctly

[jpbelang]

This is because of subtypes are not handled correctly.

Faulty code is here

    private Shape findParentType(Shape typeDeclaration) {
        if (typeDeclaration instanceof NodeShape) {
            NodeShape otd = (NodeShape) typeDeclaration;
            return otd.inherits().size() > 0 ? otd.inherits().get(0) : otd;
        } else {
            return typeDeclaration;
        }
    }

This returns the wrong type.